2-Keto-L-Gulonic acid is an important intermediate in vitamin C manufacture. Condensation of L-sorbose with acetone in the presence of sulfuric acid followed by oxidation with permanganate and hydrolysis of the diisopropylidene derivative by boiling yields 2-keto-L-gulonic acid as described in Helv. Chim. Acta. 17, 311 (1934) and U.S. Pat. No. 2,301,811. The preparation of 2-keto-L-gulonic acid by careful oxidation of L-sorbose with nitric acid is claimed in British Pat. No. 443,901 and Dutch Pat. No. 59,584. The selective reduction of 2,5-diketogluconic acid to yield a mixture of 2-ketogluconic acid and 2-ketogulonic acid with subsequent hydrolysis of the 2-ketogulonic acid to afford ascorbic acid is described in co-pending application, Ser. No. 843,946, filed Oct. 20, 1977.